Setup LayerTree class, refactor 2 functions from LayerTreeHost to it.

cc/trees/layer_tree_host.h

Index: cc/trees/layer_tree_host.h
diff --git a/cc/trees/layer_tree_host.h b/cc/trees/layer_tree_host.h
index 5628309c5456a558f5d3bfd0a65ae6bc504fae54..bbfa7cb8ee4a7f141ab73408d163d00a0706d323 100644
--- a/cc/trees/layer_tree_host.h
+++ b/cc/trees/layer_tree_host.h
@@ -40,6 +40,7 @@
 #include "cc/resources/scoped_ui_resource.h"
 #include "cc/surfaces/surface_sequence.h"
 #include "cc/trees/compositor_mode.h"
+#include "cc/trees/layer_tree.h"
 #include "cc/trees/layer_tree_host_client.h"
 #include "cc/trees/layer_tree_settings.h"
 #include "cc/trees/mutator_host_client.h"
@@ -295,9 +296,7 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
   TaskRunnerProvider* task_runner_provider() const {
     return task_runner_provider_.get();
   }
-  AnimationHost* animation_host() const { return animation_host_.get(); }
-
-  bool in_paint_layer_contents() const { return in_paint_layer_contents_; }
+  AnimationHost* animation_host() const;
 
   // CreateUIResource creates a resource given a bitmap.  The bitmap is
   // generated via an interface function, which is called when initializing the
@@ -355,13 +354,8 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
   void AddToElementMap(Layer* layer);
   void RemoveFromElementMap(Layer* layer);
 
-  void AddLayerShouldPushProperties(Layer* layer);
-  void RemoveLayerShouldPushProperties(Layer* layer);
-  std::unordered_set<Layer*>& LayersThatShouldPushProperties();
   bool LayerNeedsPushPropertiesForTesting(Layer* layer);
 
-  void RegisterLayer(Layer* layer);
-  void UnregisterLayer(Layer* layer);
   // MutatorHostClient implementation.
   bool IsElementInList(ElementId element_id,
                        ElementListType list_type) const override;
@@ -426,6 +420,9 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
     return client_picture_cache_ ? client_picture_cache_.get() : nullptr;
   }
 
+  LayerTree* GetLayerTree() { return &layer_tree_; }
+  const LayerTree* GetLayerTree() const { return &layer_tree_; }
+
  protected:
   LayerTreeHost(InitParams* params, CompositorMode mode);
   void InitializeThreaded(
@@ -560,16 +557,12 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
   EventListenerProperties event_listener_properties_[static_cast<size_t>(
       EventListenerClass::kNumClasses)];
 
-  std::unique_ptr<AnimationHost> animation_host_;
-
   std::unique_ptr<PendingPageScaleAnimation> pending_page_scale_animation_;
 
   // If set, then page scale animation has completed, but the client hasn't been
   // notified about it yet.
   bool did_complete_scale_animation_;
 
-  bool in_paint_layer_contents_;
-
   int id_;
   bool next_commit_forces_redraw_;
 
@@ -593,19 +586,16 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
 
   PropertyTrees property_trees_;
 
-  using LayerIdMap = std::unordered_map<int, Layer*>;
-  LayerIdMap layer_id_map_;
-
   using ElementLayersMap = std::unordered_map<ElementId, Layer*, ElementIdHash>;
   ElementLayersMap element_layers_map_;
 
-  // Set of layers that need to push properties.
-  std::unordered_set<Layer*> layers_that_should_push_properties_;
-
   uint32_t surface_client_id_;
   uint32_t next_surface_sequence_;
   uint32_t num_consecutive_frames_suitable_for_gpu_ = 0;
 
+  // Layer tree that hold layers.
+  LayerTree layer_tree_;
+
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHost);
 };